A sensor network system includes many sensor devices (also called sensor modules) each having a wireless communication function. The sensor network system is used for various purposes in every field, for example, crime-prevention, nursing care, energy conservation, wide area measurement, or tracing.
For example, in the field of nursing care, with sensor devices, a ventricular rate, a body temperature, posturing, moves of limbs, a state of emergency, and the like of a cared person can be monitored. Moreover, for example, in building environment, with sensor devices, earthquake data, moves of a structural support section, fire disaster, flood and the like can be checked.
Furthermore, for example, in home applications, the sensor network system is considered to be used for various purposes such as home security, monitor/control of appliances, watch/nursing care, remote management, and the like.
The sensor devices are set in a wide area. Moreover, a case in which a large number of the sensor devices are additionally set is easily expected because of good installation capability of the sensor devices. When the sensor network system is used in home applications, the sensor devices are additionally set and many sensor devices are set inside/outside of a building, because of the good installation capability of the sensor devices.
Accordingly, in order to reduce trouble of a manager, it is preferable that communication paths of the many sensor devices set are autonomously established. The autonomy is an important factor in the sensor network system.
Regarding a conventional method of establishing a communication path, Japanese Unexamined Patent Publication No. 94530/2005 (Tokukai 2005-94530) (published on Apr. 7, 2005) discloses a method of autonomously establishing a network of wireless devices with one base station at the center.
Moreover, Japanese Unexamined Patent Publication No. 157744/2005 (Tokukai 2005-157744) (published on Jun. 16, 2005) discloses a method of autonomously establishing a wireless network by detecting other devices such as facility control means, a center server, or a mobile terminal device, each existing in a predetermined communication distance set in advance.